1. Technical Field of the Invention
The present invention relates to operation and maintenance (OAM) activities within a cellular communications network and, in particular, to the specification of OAM flows for A-interface connections.
2. Description of Related Art
Reference is now made to FIG. 1 wherein there is shown a schematic diagram of a cellular telephone network 10 including a plurality of interconnected switching nodes (SN) 12. Although only two switching nodes 12 are shown, it will be understood that the network 10 likely includes many more interconnected nodes. The first and second switching nodes 12(1) and 12(2) may comprise any one of a number of known telecommunications switching devices, including mobile switching centers (MSC""s), as commonly used and known in the art for providing either digital or analog cellular telephone service to a plurality of mobile stations (MS) 14. The switching nodes 12 are interconnected with each other for communication via both voice trunks 18 (illustrated with broken lines) and signaling links 16 (illustrated with solid lines) providing a known ISUP (or R1 or R2) type connection. The voice trunks 18 provide voice and data communications paths used to carry subscriber communications between the switching nodes 12. The signaling links 16 carry command signals between the switching nodes 12. These signals may be used, for example, in setting up and tearing down voice and data communications links over the voice trunks 18 and controlling the provision of calling services to the mobile stations 14. The switching nodes 12 are also connected to a data base 20 comprising a home location register (HLR) by means of signaling links 22 providing a known Mobile Application Part (MAP) or IS-41 type connection. The data base 20 stores information concerning the mobile stations 14 comprising location information and service information.
Each of the switching nodes 12 is further connected to at least one associated concentration point (CP) 24 via both a signaling link 26 and a voice trunk 28. The voice trunk 28 provides a voice and data communications path used to carry subscriber communications between each switching node 12 and its associated one or more concentration points 24. The signaling link 26 carries command signals between the node 12 and its associated concentration point 24. The signaling link 26 and trunk 28 are collectively commonly referred to in the art as the xe2x80x9cA interfacexe2x80x9d. Each concentration point 24 is then connected to a plurality of base stations (BS) 30 which operate to effectuate radio frequency communications with proximately located mobile stations 14 over an air interface 32.
As a basic functionality, each concentration point 24 performs necessary switching operations to route communications (traffic or control) between the signaling link 26 and trunk 28 and the base stations 30. As an enhanced functionality, each concentration point 24 may further perform radio network control (RNC) operations (such as mobile station locating, radio frequency channel allocation, handoff control, and local mobile station to mobile station call set-up) in a well known manner to control mobile radio frequency communications operation. When both the basic and enhanced functionalities are present, the concentration point 24 is referred to in the art as a base station controller (BSC). When both functionalities are not present, typically the concentration point 24 routes, and the switching nodes 12 implement the radio network controller operations.
The concentration points 24 may also be interconnected with each other via both a signaling link 34 and a voice trunk 36. The voice trunk 36 provides a voice and data communications path used to carry subscriber communications between the concentration points 24. The signaling link 34 carries command signals between the concentration points 24. The signaling link 34 and trunk 36, when present, are included within the xe2x80x9cA interfacexe2x80x9d. These connections are advantageously utilized in certain situations (such as at intra-switching node handoff or mobile station to mobile station call set-up) to by-pass the switching node 12 and more efficiently support the provision of cellular service to the mobile stations.
Although direct communications links (signaling and/or trunk) are illustrated in FIG. 1, it is understood by those skilled in the art that the links are not necessarily direct between the illustrated nodes, and may instead pass through many other communications nodes (not shown) of the mobile network, and perhaps even utilize other communications networks (such as the public switched telephone networkxe2x80x94PSTN). Illustration of the links in the xe2x80x9cvirtualxe2x80x9d manner shown in FIG. 1 is therefore by way of simplification of the drawing. The cellular telephone network 10 may comprise a Global System for Mobile (GSM) communications, an Advanced Mobile Phone System (AMPS), a digital Advanced Mobile Phone System (D-AMPS), a code division multiple access (CDMA) system, or the like.
Prior to the definition of the A-interface, the connection between the switching node 12 and concentration point 24 was proprietary and vendor specific. This forced a cellular service operator/provider to purchase all the equipment from the same source. The premise behind the development of the A-interface concept is to support a multi-vendor environment for cellular network equipment. With the specification of a standardized interface between the switching nodes 12 and the concentration points 24, a cellular service operator/provider could purchase its needed equipment from different vendors and easily interconnect that equipment.
The Telecom Industry Association (TIA) sub-committee TR45.4 is currently finalizing a definition for the A-interface (see, Interim Standard IS-634, rev. A). This standard describes the overall system functions between the switching nodes 12 and the concentration points 24 relating to the services and features required for the interface.
The A-interface includes a plurality of sub-interfaces. A first sub-interface (A1) carries signaling (see, signaling link 26) through the concentration point 24 between a call control (CC) function and mobility management (MM) function within the switching node 12 and the call control (CC) component of the base station 30. The A1 sub-interface supports short message service (SMS) messaging and over the air activation service provisioning (OTASP) using OTA data messages as defined in Interim Standard IS-683 sections 3.5 and 4.5. A second sub-interface (A2) carries 64 kbit/sec pulse code modulation (PCM) information (voice/data) over the trunk 28 between the switch component of the switching node 12 and either the channel element component of the base station 30 (for an analog air interface) or the selection/distribution unit (SDU) of the base station 30 (for a digital air interface). A third sub-interface (A3) carries coded user information (voice/data) frames and signaling between the selection/distribution unit (SDU) and the channel element component of the base station 30. The A3 sub-interface is composed of two parts: a signaling connection; and a user traffic connection. The signaling connection is carried across a separate logical path from the user traffic connection and controls the allocation and use of the logical paths for user traffic connections. A fourth sub-interface (A4) carries signaling between the call control component (CC) and the selection/distribution unit (SDU) of the base station 30. The A3 sub-interface is utilized to carry traffic between two concentration points 24 over the trunk 36. The A4 sub-interface is utilized to carry signaling between two concentration points 24 over the signaling link 34. A fifth sub-interface (A5) carries a full duplex stream of bytes between the inter-working function (IWF) of the switching node 12 and the selection/distribution unit (SDU) of the base station 30.
One important aspect of network operation that is not well defined by IS-634 rev. A is the provision of operation and maintenance (OAM) flows for user data and signaling over the A-interface. More particularly, there is a need for an OAM flow support for transport optimization and improved application support over the A1, A2, A3 and A4 sub-interfaces.
Reference is now made to FIG. 2 wherein there is shown a block diagram for a synchronous optical network (SONET) 60 providing the transport layer (physical) of an OSI seven layer model for communications systems. The SONET 60 includes a plurality of repeaters 62. The flow of operation and maintenance information between repeaters 62 in the SONET 60 is referred to in the art as an F1 OAM flow 64. The F1 OAM flow is the smallest recognizable physical entity for OAM information transmission. When a number of repeaters 62 are collected together to define a transmission path, this forms a section 66. The flow of operation and maintenance information between end-point repeaters 62 for a section 66 in the SONET 60 is referred to in the art as an F2 OAM flow 68. When a number of sections 66 are collected together to define a transmission path, this forms an end-to-end system 70. The flow of operation and maintenance information between end-points 72 of the system 70 in the SONET 60 is referred to in the art as an F3 OAM flow 74.
Reference is now made to FIG. 3 wherein there is shown a block diagram for an asynchronous transport mode (ATM) network 80 (which may, for example, run over SONET 60 as in FIG. 2). In this configuration, ATM comprises the data link layer of the OSI seven layer model for communications systems. The flow of operation and maintenance information between end-points 78 of an ATM network 80 in connection with a virtual path (VP) 82 is referred to in the art as an F4 OAM flow 84. Similarly, the flow of operation and maintenance information between end-points 78 of an ATM network 80 in connection with a virtual circuit (VC) 86 is referred to in the art as an F5 OAM flow 88.
There may occur instances where OAM functionalities are required at the ATM adaptation layer (AAL), which comprises the network layer of the OSI seven layer model for communications systems. This OAM functionality can be supported by the existing F4 OAM flow 84 and F5 OAM flow 88 if the ATM connection (with the AAL packets) is terminated at the same end-points 78 of the ATM network 80 using either the virtual path 82 or virtual circuit 86. When, for example, a number of end-to-end SONET systems 70 are collected together to define a transmission path and form an end-to-end ATM network 80, AAL packets may be relayed (multiplexed/demultiplexed) at SONET end-points 72 to different locations. In this configuration, the existing F4 OAM flow 84 and F5 OAM flow 88 cannot support an end-to-end OAM functionality, and thus cannot be used. There is a need then in the art for a new type of OAM flow for use in connection with providing an end-to-end OAM functionality for AAL packet transmissions (traffic/signaling) within an end-to-end ATM network 80.
With additional reference now once again to FIG. 1, another concern arises with respect to OAM flow support over the A-interface. Again, OAM functionality can be supported by the existing F4 OAM flow 84 and F5 OAM flow 88 if the ATM connection (with the AAL packets) is terminated at the same A-interface end-points 78 using either the virtual path 82 or virtual circuit 86, and assuming that ATM is supported for use on each of the A1-A4 sub-interfaces. This is not necessarily the case, however, as the current IS-634 rev. A proposal specifies ATM for use only on the A3 and A4 sub-interfaces. The A1 and A2 sub-interfaces conversely utilize a 64 kits/sec digital signal level O (DSO) based transport which cannot support either an F4 OAM flow 84 or an F5 OAM flow 88 as currently defined. Thus, there is a need in the art for a new type of OAM flow for use in connection with providing an end-to-end OAM functionality for transmissions (traffic/signaling) over the A-interface with respect to DSO base transports.
To address the foregoing needs, the present invention defines a pair of new OAM flows for use in connection with providing an end-to-end OAM functionality for transmissions (traffic/signaling) of the A-interface within an end-to-end network. The flow of operation and maintenance information between network layer end-points of the network in connection with A-interface signaling transmissions (DSO or AAL) comprises an F6 OAM flow. In connection with A-interface operation, this F6 OAM flow is utilized for OAM functionality over the A1 and A4 sub-interfaces. Similarly, the flow of operation and maintenance information between network layer end-points of the network in connection with traffic transmissions (DSO or AAL) comprises an F7 OAM flow. In connection with A-interface operation, this F7 OAM flow is utilized for OAM functionality over the A2 and A3 sub-interfaces.